Method of controlling thread tension



Jan. 3, 1950 M. MOONEY METHOD OF CONTROLLING THREAD TENSION Filed July18, 1946 ATTORNEY Patented Jan. 3, 1950 METHOD OF CONTROLLING THREADTENSION Melvin Mooney, Lake Hiawatha, N. J., assignor to United StatesRubber Company, New York, N. Y., a corporation of New Jersey ApplicationJuly 18, 1946, Serial No. 684,602

9 Claims.

The present invention relates primarily to a novel method of controllingthe tension of a rubber thread as it is Wound upon the core of a golfball, but the invention can be employed to control the tension ofthreads, cords, wires or filaments of various materials.

In manufacturing the better grade golf balls it is endeavored to windthe rubber thread on the golf ball core with the highest tension thatcan be used without producing breakage of the rubber thread during thewinding operation, or within the ball after the core is wound. Themaximum possible tension in the thread is desired because tests haveshown that the higher the winding tension, the higher the resilience andthe longer the flight of the ball when driven with a golf club. Howevergolf ball thread cannot be made absolutely uniform in cross section bythe methods now in use. The best that could be done with theconventional thread controlling apparatus available heretofore totension the thread during the golf ball winding operation was to adjustthe tensile force upon the thread to'such a value that a small tolerablenumber of breaks occurred, while at the same time much of the thread wasWound on the core at a tension less than the desired high tension. Inother words the practice heretofore has been to windthe rubber thread onthe core under a selected constant load, but the load must be chosen notto overstretch those portions of the thread that happen to beundersized, with the result that those portions of the thread thathappen to be oversized are understretched. In the finished ball thetension of the thread is therefore less in some regions than it shouldbe.

The purpose of the present invention-"is to change the control of thetension of the thread being wound from one of tensile force to one oftensile stress. If the tensile force is continuously adjusted tomaintain the tensile stress constant, a high mean stress can be utilizedwith a minimum of thread breakage, and a golf ball will be produced thatis uniformly high as to thread tension.

While, as above stated, the present invention was developed primarily tomaintain the tensile stress constant in highly elastic thread, such asthe rubber thread of golf balls, the method of the present invention maybe employed to maintain the tensile stress constant in threads orfilaments having a much lower degree of stretch.

The present invention makes use of the well known physical law whichstates that the natural frequency of vibration of a thread stretchedbetween two fixed points is determined by the ratio of the stretchingforce to the linear density (mass per unit length along the thread).This ratio can also be expressed as the ratio of the tensile forcestretching the thread to the product of the volume density times thecross sectional area of the thread. In the rubber thread used in windingthe body of golf balls the density is practically constant, but thecross sectional area exhibits uncontrolled variations. It follows fromthis physical law that if the tensile force is automatically andcontinuously adjusted so that the natural frequency of vibration of adefinite length of the advancing thread is held constant, then thetensile force per unit cross-section area, that is, the stress, willnecessarily be constant and can be maintained at a high value; and thisis what is desired to produce a golf ball of high resilience.

It will appear from the foregoing that if a rubber thread being woundupon a golf ball core under tension is caused to pass over two spacedpoints such as small pulleys spaced a fixed distance apart, and the freelength of thread between these two points is kept vibrating at itsnatural frequency, the rate of such vibration will vary (1) with thetension of the thread and (2) with the size of such thread.

As above pointed out it is not practical to produce a thread under thepresent methods of manufacture which will run absolutely uniform as tosize, therefore, in accordance with the present invention it is proposedto regulate the tensile force such that the natural frequency ofvibration remains substantially constant, by increasing the force whenthe thread runs over size and decreasing the force when the thread runsunder size. The effect of this will be to wind the thread under uniformtensile stress instead of under uniform tensile force as has been thepractice heretofore.

To summarize the foregoing, the present invention resides in the methodof controlling the tensile stress in an advancing thread by advancingthe stretched thread so that it passes two points spaced a fixeddistance apart, vibrating this length of thread, measuring the naturalfrequency of vibration by suitable means, and varying the tension uponthe thread in accordance with said measurement so as to maintain thenatural frequency of vibration of this length of thread substantiallyconstant.

One method for measuring the natural frequency of the thread is toimpose upon the thread a vibration, or periodic impulse, of fixedfrequency slightly diiferent from the natural frequency, and by means ofa suitable detecting device connected to an intensity meter to measurethe intensity, or the amplitude of the vibration. This method makes useof the resonance curve, which is the graph showing the amplitude of thecontinuous vibration as it varies with the frequency of the impressedvibration. Such a curve has a maximum at the natural frequency and dropssharply on both sides of the maximum. The rate at which the curve dropsas the impressed frequency departs from the natural frequency dependsupon the rate at which the vibrational energy of the thread isdissipated. Since the rate of dissipation is essentially constant for agiven system, the resonance curve remains esentially constant in form asthe thread advances; and hence the measured amplitude of continuousvibration may be used as a measure of the difference between theimpressed frequency and the natural frequency. With the impressedfrequency fixed and known, this constitutes a measurement of the naturalfrequency.

One form of apparatus applying this method in effecting automaticcontrol of thread tension is shown in the accompanying drawing wherein;

Fig. 1 is a more or less diagrammatic view of the apparatus; and

Fig. 2 is a similar view of a modified part.

The thread control mechanism herein contemplated is shown in connectionwith a golf ball winding machine having the casing l0 adapted to supportand rotate one of the golf ball winding heads I l, which head has thespaced frustro-conical disks [2 adapted to support the ball B upon whichthe rubber thread T, is being wound. The golf ball winding machinepartially illustrated in the drawing may be of the general typedisclosed in the Cobb Patent No. 1,270,009, or it may have any otherpreferred or well known construction.

The thread T being wound upon the ball B may be supplied from anysuitable source such as the spool l3 which is rotatably supported at 14upon a supporting beam l 5, and as the thread unwinds from this spool l3it passes downwardly about the floating pulley I6 and then upwardly overthe pulley I! supported by the beam l5. The pulley I6 is rotatablymounted at the outer end of a swinging arm l8 that is pivotally securedat l9 to a fixed support 20 and this arm l8 has suspended therefrom anumber of weights 2|. The rotation of the spool l3 as the thread T isunwound therefrom is retarded, in the construction shown, by the brakeband 22 which is looped about a flange or pulley connected to thisspool; one end of the brake band is anchored at 23, while the other endis secured to the rocking arm l8 at 24. The construction is such that anearly uniform tension will be placed upon the rubber thread T as itpasses upwardly around the pulley ll, since if a reduction in thetension in the thread occurs the arm l8 will swing downwardly toincrease the brake action, and as the tension upon the thread increasesthe arm will be raised to reduce the brake action.

This tension mechanism is not new and is not an essential part of thepresent invention but is preferably provided to give a preliminaryadjustment of the thread tension to approximately the desired value. Thefiner adjustment of the thread tension to the exact value desired ismade in accordance with the present invention so as to maintain thetensile stress in the thread T as it is wound on the ball Bsubstantially constant within narrow limits in spite of variations inthread size. This is accomplished in the construction shown by providingthe thread contacting drum 25 which is rotatably supported by the beam26. The thread T may be looped around an idler roll 25 to increase thelength of contact with the drum 25, thus to prevent it from slipping.The drum 25 has rigidly secured thereto the brake wheel 21 about whichthe brake band 28 is looped. One end of this brake band is anchored at29 and the other end is secured to the iron armature or core 30 whichmoves up and down in the electromagnet coil 3| which is supported in afixed position by the support 32.

The friction which the brake band 28 exerts upon the brake drum 2! iscontrolled, in accordance with the present invention, so as to maintainthe frequency at which the portion of the thread T vibrates between twofixed points substantially constant. To this end in the constructionshown the freely turning rollers 34 and 35 are provided, at a fixeddistance apart, so that the tensioned thread will pass over theserollers as it approaches the ball B being wound. Various means may beprovided to keep the length of thread B extending between these pulleys34 and 35 vibrating.

In order to vibrate this length of thread at a fixed frequency near thedesired natural frequency, the pulley 34 may be rotatably supported byan upright 36 that is mounted on a spring arm 31 such as a metal bar oneend of which is rigidly secured at 38 to the supporting frame 39. Thespring 31 carries the weight 31 which can be adjusted in its horizontalposition so as to give the desired natural frequency of vibration of thespring. Means should be provided for causing the arm 3'! to vibrate atits natural frequency, and the means shown to this end comprise thefixed solenoid coil which is disposed below the arm as shown. Anarmature 43, which is attached to one face of the arm 31, projects intoand terminates within the coil 4!. Attached to the other side of thespring arm 31 is the short leaf spring 40, on which is mounted themicrophone button 42. The microphone 42 and the coil M are connected inseries through the circuit 44 to a source of constant D. C. voltage. Thespring arm is thus maintained in vibration at a frequency determined bythe adjustable weight 31 and at an amplitude determined by theadjustable voltage connected through the line 44. If, for example, thedesired natural frequency of the thread is 1000 vibrations per second,the frequency of the spring arm would be adjusted to that slightlylarger value, perhaps 1050, for example, which is at or near the pointof greatest slope of the resonance curve for a rubber thread of naturalfrequency 1,000. This frequency of greatest slope in the resonance curveis likewise that fixed impressed frequency for which the amplitude of arubber thread of adjustable natural frequency increases most rapidly asthe natural frequency is increased above 1,000. Under these conditionsthe amplitude of vibration of the thread, as previously stated, willincrease rapidly as its natural frequency approaches that of theconstant imposed frequency, and will decrease rapidly as the differencebetween the imposed frequency and natural frequency increases.Therefore, under these conditions the amplitude of the thread vibrationis a sensitive measure of the natural frequency of the thread at anyinstant, and of variations in the natural frequency.

The frequency of the thread vibration at any instant may be determined,according to one method, by using a microphone to detect the sound ofthe vibrating thread and measuring the sound frequency with a suitablefrequency meter.

In the construction shown the amplitude of the thread vibration ismeasured in the following manner. The pulley 35 is rotatably mounted ona post 45 which is secured to the flat spring 46 mounted on thesupporting frame 39. The post 45 has attached thereto a dynamicmicrophone pick-up 41. In this arrangement the angle at which thevibrating rubber thread approaches pulley 35 varies periodically withthe thread vibrations. As a result of this periodic variation in angle,there is also a periodic variation in the vertical component of theforce exerted by the thread on the pulley 35. This periodic verticalforce of the thread has an amplitude which is proportional to theamplitude of vibration of the thread; and it will therefore cause thepulley 35 and post 45 to vibrate with an amplitude which is proportionalto the amplitude of vibration of the thread. The signal from the pick-uptherefore will be proportional to the amplitude of vibration of thethread. In the construction shown the signal from the pick-up 41 passesby means of the wires 48 to the amplifier 49, and after having beenamplified, passes to the rectifier 50, and thence by the wires to thesolenoid coil 3| above mentioned.

In order to operate the system described, the

- combined braking force due to the two weights 2| and 33, is adjustedso that the tensile force exerted upon the thread with no current in thecoil 3| will be slightly greater than the tensile force which will berequired for the thickest part of the rubber thread T being wound. Then,when the thread is first started winding on the ball B, the tension,starting at a low value, will build up as the rubber thread between thesupply spool I3 and ball B is stretched without any movement of thespool l3. During this time the natural frequency of the thread Will lieat some point below the frequency at which the pulley 34 is beingvibrated by the coil 4|, and the amplitude of the thread vibration atthis time will have a low value. When however the thread tensionincreases to such extent that the natural frequency approaches moreclosely the impressed frequency, the amplitude of thread vibration, andso of the microphone signal at 41, will both increase rapidly. Theamplifier 49 should be adjusted so that the lifting force of the core 30will be just sufficient to let the pulley 25 turn at a constant speedwhen the natural frequency of the thread has attained its predetermineddesired value. The amplitude of thread vibration will at this time bemost sensitive to small changes in its natural frequency, as previouslyexplained. With this adjustment, if the thread stress becomes too great,due to a local decrease in the thread section, so that the naturalfrequency approaches more closely that of the imposed frequency theamplitude of thread vibration will increase, and this will cause anincrease in the lifting force of the core 30. The upward movement ofthis core will decrease the braking action on the drum 21 and permit atemporary increase in the velocity of rotation of the pulley 25 tothereby reduce the tension on the rubber thread. Similarly, a slightlocal increase in thread-section will result in an increase in brakingaction at 21 to temporarily retard rotation of the drum 25 to increasethe thread tension. If this automatic action keeps the amplitude ofthread vibration within narrow limits, the natural frequency will bemaintained nearly constant, which is what is desired to keep the tensilestress of the thread being wound upon the ball approximately constant.

While the means just described for automatically controlling the tensionof the thread T, or other automatic means to this end, is consideredhighly desirable, such automatic feature is not essential in allembodiments of the invention. For example, the brake controlling core 30and coil 3| could be omitted and an ammeter 52 could be connected to therectifier 5|] to thereby indicate visually to the machine operatorvariations in the electric energy from the pick-up 41. With this visualreading the operator could manually adjust the brake band .28 to varythe tension of the thread T.

It will be seen from the foregoing that as the running thread T passesover the spaced pulleys 34 and 35 the natural frequency of vibration ofthis portion of the thread will be continuously measured either directlyor indirectly, and the tensile force opposing the winding action will becontinuously adjusted to keep the natural frequency constant withinnarrow limits, to thereby control the tensile stress of the windingthread independently of variations in its size and elastic modulus. Inpracticing the present method it is important that the velocity at whichthe thread T advances be kept sufficiently small that the distancetraversed during one cycle of vibration will be small compared with thedistance between the pulleys 34 and 35. This is equivalent to sayingthat the velocity of advance must be kept small compared with thevelocity of propagation of a wave form along the stretched thread.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

l. The method of controlling the tensile stress in an advancing thread,which consists in advancing the thread under tension past two pointsspaced a fixed distance apart, vibrating the free portion of the threadbetween these points to set up periodic variations in the force exertedby the thread on one of said points, detecting variations in the saidperiodic force of the thread at such point due to changes in theamplitude of the thread vibrations, and adjusting the tensile force onthe thread in accordance with the detected variations to thereby holdthe natural frequency of vibration substantially constant, thereby tokeep the tensile stress substantially constant in spite of variation inthe size and elastic modulus of the advancing thread.

2. The method of controlling the tensile stress in an advancing thread,which consists in advancing the thread under tension past two pointsspaced a fixed distance apart, impressing a vibration of fixed frequencyon the free portion of the thread between these points, measuringvariations in the natural frequency of vibration of this portion of thethread by measuring variations in the amplitude of the impressedvibration, and varying the tension upon the thread in accordancetherewith so as to keep the natural frequency of this portion of thethread practically constant, thereby to keep the tensile stress in thethread substantially constant and independent of variations in the sizeof the advancing thread.

3. The method of controlling the tensile stress in an advancing thread,which consists in advancing the thread under tension past two pointsspaced a fixed distance apart, vibrating the thread between these pointsto set up periodic variations in the force exerted by the thread on oneof said points, continuously detecting variations in the said periodicforce of the thread at said point caused by changes in the amplitude ofthe thread vibration, and continuously adjusting the tension on thethread in accordance with such detected variations to hold the naturalfrequency substantially constant at a selected value, to thereby keepthe pounds per square inch tension of the thread constant at apredetermined value.

4. The method of controlling the tensile stress in an advancing thread,which consists in advancing the thread under tension past two pointsspaced at fixed distance apart so that it may vibrate, subjecting thisportion of the thread to a vibration of fixed frequency slightlydifferent from the desired natural frequency and measuring variations inthe natural frequency of the thread as evidenced by changes in theamplitude of thread vibrations, and adjusting the tension upon thethread in accordance therewith so as to keep the natural frequency ofthis portion of the thread practically constant at a predeterminedvalue, thereby to keep the tensile stress substantially constant at apredetermined value in spite of variation in the size and elasticmodulus of the advancing thread.

5. The method of controlling the tensile stress in an advancing thread,which consists in advancing the thread under tension past two pointsspaced a fixed distance apart, vibrating the free portion of the threadbetween these points at its approximately natural frequency, detectingthe intensity of the periodic force which such vibrating thread exertsat one of said points, and adjusting the tensile force on the thread inaccordance With this intensity to hold the frequency of thread vibrationsubstantially constant, thereby to keep the tensile stress in the threadsubstantially constant and independent of variations in the size of theadvancing thread.

6. The method of controlling the tensile stress in an advancing thread,which consists in advancing the thread under tension past two pointsspaced a fixed distance part, vibrating the free portion of the threadbetween these points at its approximately natural frequency, detectingchanges in the periodic force which such vibrating thread exerts at oneof said points, and automatically adjusting the tensile force on thethread as such changes are detected to hold the frequency substantiallyconstant, thereby keeping the tensile stress in the thread substantiallyconstant.

7. The method of controlling the tensile stress in an advancing thread,which consists in advancing the thread under tension past two pointsspaced a fixed distance apart, impressing on the free portion of thethread a vibration of a frequency slightly different from the naturalfrequency corresponding to the desired tensile stress,

measuring the amplitude of the vibration, using it as ameasure of-thenatural frequency of vibration and adjustingthe tensile force inaccordance therewith to keep the natural frequency substantiallyconstant, thereby keeping the tensile stress substantially constant.

8. The method of controlling the tensile stress in' an advancing thread,which consists in advancing the thread under tension past two pointsspaced a fixed distance apart, vibrating the thread between these pointsso that the force periodically exerted by it upon one of the points willvary with changes in its amplitude of vibration, electrically detectingvariations in the periodic force of the thread at said point, andautomatically adjusting the tension of the thread in accordance withsuch detected variations, thereby keeping the tensile stress of thethread at a selected value.

9. The method of controlling the tensile stress in an advancing thread,which consists in 'advancing the thread under tension past two pointsspaced a fixed distance apart, vibrating the thread between these pointsso that the force periodically exerted by it upon one of the points willvary with changes in its amplitude of vibration, electrically detectingby a microphone pickup the variations in the periodic force of thethread at-said point, and. automatically adjusting the tension of thethread in accordance with such detected variations, thereby keeping thetensile stress of the thread at a selected value.

MELVIN MOONEY.

REFERENCES CITED UNITED STATES PATENTS Name Date Wilhelm Aug. 19, 1947Number

